SRF Phosphorylation by Glycogen Synthase Kinase-3 Promotes Axon Growth in Hippocampal Neurons

Abstract

The growth of axons is an intricately regulated process involving intracellular signaling cascades and gene transcription. We had previously shown that the stimulus-dependent transcription factor, serum response factor (SRF), plays a critical role in regulating axon growth in the mammalian brain. However, the molecular mechanisms underlying SRF-dependent axon growth remains unknown. Here we report that SRF is phosphorylated and activated by GSK-3 to promote axon outgrowth in mouse hippocampal neurons. GSK-3 binds to and directly phosphorylates SRF on a highly conserved serine residue. This serine phosphorylation is necessary for SRF activity and for its interaction with MKL-family cofactors, MKL1 and MKL2, but not with TCF-family cofactor, ELK-1. Axonal growth deficits caused by GSK-3 inhibition could be rescued by expression of a constitutively active SRF. The SRF target gene and actin-binding protein, vinculin, is sufficient to overcome the axonal growth deficits of SRF-deficient and GSK-3-inhibited neurons. Furthermore, short hairpin RNAmediated knockdown of vinculin also attenuated axonal growth. Thus, our findings reveal a novel phosphorylation and activation of SRF by GSK-3 that is critical for SRF-dependent axon growth in mammalian central neurons.

Vinculin mediated axon growth requires interaction with actin but not talin

“…1C, D). This was consistent with an earlier finding in which shRNAmediated knockdown of vinculin was shown to attenuate axon growth in cultured hippocampal neurons (Li et al, 2014). Next, we asked whether vinculin deletion also affected axon growth in vivo.…”

“…Vinculin-deficient fibroblasts showed poor adhesion to substrate, less spreading, enhanced cell migration and cytoskeletal dynamics (Coll et al, 1995;Demali, 2004;Thievessen et al, 2013;Xu et al, 1998b). Vinculin has been shown to be important for filopodia and lamellipodia stability, neurite outgrowth and axon growth in vitro (Li et al, 2014;Sydor et al, 1996;Varnum-Finney & Reichardt, 1994). Despite these studies, the requirement for vinculin and the role of different functional domains of vinculin for neuronal migration and axon growth in vivo is poorly understood.…”

Simvastatin Attenuates Neurogenetic Damage and Improves Neurocongnitive Deficits Induced by Isoflurane in Neonatal Rats

“…After phosphoinositide-dependent protein kinase (PDK) phosphorylating Akt-1, GSK-3β, a serine/threonine kinase, is inhibited [52]. Studies have demonstrated that GSK-3β played an important role in fundamental functions of cell such as cell cycle, cytoskeletal integrity, dendritic growth, axon growth and neuronal differentiation [53,54]. Isoflurane induced neuroapoptosis and synaptogenesis impairment by decreasing ribosomal protein S6 activity through suppression of upstream IGF-1/MEK/ERK and IGF-1/PI3K/Akt signaling [55].…”

Overexpression of Serum Response Factor in Neurons Restores Ocular Dominance Plasticity in a Model of Fetal Alcohol Spectrum Disorders

“…During development of the nervous system, SRF plays a major role in neuronal migration, axon guidance and myelination (Chai and Tarnawski, 2002; Alberti et al, 2005; Knoll et al, 2006; Wickramasinghe et al, 2008; Li et al, 2014). Also, several studies have shown that SRF can mediate neuronal plasticity through the expression of neurotrophins, immediate early genes, cytoskeletal proteins and thrombospondins (Morris et al, 1999; Chai and Tarnawski, 2002; Schratt et al, 2002; Christopherson et al, 2005; Ramanan et al, 2005; Knoll et al, 2006; Stritt et al, 2009).…”